Supply of heat to fluidized solids beds for the production of fuel gas



NOV. 25, 1952 c E HEMNHNGER 2,619,415

SUPPLY OF HEAT TO FLUIDIZED SOLIDS BEDS FOR THE PRODUCTION OF FUEL GAS Filed Aug. 15, 1946 5 Sheets-Sheet l Pnonucew.

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QEAcn u e Charles EJ-Zemmz'ngef Sax/Qatar bi-SMOJLID o r 1:2. as

Nov. 25, 1952 c. E. HEMMINGER 2,619,415 SUPPLY OF HEAT TO FLUIDIZED SOLIDS BEDS FOR THE PRODUCTION OF FUEL. GAS Filed Aug. 15, 1946 3 Sheets-Sheet 2 Pacbucr 22,5 9%

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Ens (lbboQ-neg NOV. 25, 1952 c, HEMMlNGER 2,619,415

SUPPLY OF HEAT TO FLUIDIZED SOLIDS BEDS FOR THE PRODUCTION OF FUEL GAS Filed Aug. 15, 1946 3 Sheets-Sheet I5 Charles E. Wemminser E3nver2bor' figMCLbborrieg Patented Nov. 25, 1952 SUPPLY OF HEAT TO FLUIDIZED SOLIDS BEDS FOR THE PRODUCTION OF FUEL GAS Charles E. Hemminger, Westfield, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application August 15, 1946, Serial No. 690,818

8 Claims.

' The present invention relates to the supp of heat to dense turbulent beds of finely divided solids fluidized by an upwardly flowing gas. More particularly, the invention is concerned with the supply of heat to the conversion of carbonaceous materials such as all types of coal, coke, lignite, peat, cellulosic materials'including lignin, oil shale, tar sands, petroleum, heavy residues, pitch, asphalt, and the like as Well as liquid and gaseous hydrocarbons, into volatile fuels and valuable gases employing the fluid solids technique. I

The application of the so-called fluid solids technique to the conversion of solid carbonaceous materials into volatile fuels, for example to the carbonization of carbonizable materials or the gasification of solid fuels is well known in the art. In these processes finely divided carbonaceous materials, such as coal, having a fluidizable particle size of say about 50-400 mesh are fed to a conversion zone wherein they are maintained, at conversion temperature, in the form of a dense turbulent bed of finely divided solids fluidized by an upwardly flowing gas to form a well-defined upper level.

Most of these conversions, particularly the carbonization of carbonizable fuels and the manufacture of water gas by reactingsolid fuels with steam, are endothermic processes. j Various methods of supplying the heat required'in these processes have been suggested.

One method utilizes the sensible heat'pf heatcarrying gases such as steam, flue gases, make gas, etc. blown through the fluidized bed of carbonaceous solids. low heat capacity of the gases as compared with that of the solids to be heated, vast amounts of heating gases having a temperature considerably higher than that of the desired conversion must be applied. While this method maygfibe commercially feasible for low temperature" carbonizations carried out at temperatures of about 800-12-00 F. the high gas-preheating temperatures required for high temperature carbonization and water gas manufacture are generally prohibitive because of the limited heat resistance of suitable furnace materials. In addition, the heating gas complicates the recovery of the desired volatile conversion products or lowers the heating value of the product gas or both.

Some of the disadvantages of this method may be avoided when the necessary heat is supplied by means of a limited combustion Within the fluidized bed of carbonaceous solids. However,

this method entails the loss of considerable proportions of valuable combustible conversion prod- As a result of the" extremely ucts which are burnt in the course of the limited combustion. Moreover, the dilution of the prod uct gases by gaseous combustion products constitutes a serious disadvantage of this procedure.

Another method of heat supply involves the use of a separate fluid combustion zone from which highly heated finely divided solid combustion residue is circulated to the heat-consuming conversion zone. Aside from the fact that an additional combustion reactor of considerable dimensions is required, the eficiency of heat generation by this type of combustion is low because of the high carbon monoxide formation in a fiuid" vessel heated by combustion with air. Moreover, enormous solids circulation rates are required, particularly at high conversion temperatures which necessitate small temperature differences between the combustion and the conversion zone because of limitations imposed by the heat resistance of the construction material and the fusion or softening point of the ash. When applied to carbonization, the product coke must be separated from the relatively worthless solid heat carrier to obtain a marketable product.

Internal heating of the fluid bed by various electrical means has been suggested but is impractical because of technical and economical,

inefiiciencies such as the requirement of cheap,

power as oiT-peak hydroelectric power, reaction Q of H20 and C02 with ordinary types of electrodes. such as carbon, slagging of ash on metallic electrodes, etc.

Similar difficulties arise in the endothermic conversion, of hydrocarbons with steam ,into water gas with the aid of fluid reformed catalysts and in various other endothermic processes employing the fluid solids technique.

The present invention overcomes the aforementioned difiiculties and affords various addi tional advantages as will be fully understood from the following detailed description read with reference to the accompanying drawing.

It is, therefore, the principal object of the present invention to provide improved means for supplying heat to dense turbulent beds of finely divided fluidized solids.

Another object of this invention is to provide improved means for supplying the heat required by the conversion of carbonaceous materials into volatile combustibles employing the fluid solids technique, without the disadvantages discussed above.

A more specific object of the invention is to provide improved means for supplying the heat required in the carbonization of carbonizable fuels employing the fluid solids technique to produce volatile fuels and coke without the disadvantages discussed above.

A further specific object of the invention is to provide improved means for supplying the heat required in the production of fuel gases from solid carbonaceous materials, employing the fluid solids technique, without the disadvantages discussed above.

Other and further objects will become apparent from the following disclosure and claims.

The aforementioned objects and advantages may be accomplished in accordance with the present invention quite generally by supplying to the fluidized solids bed the heat of a fluid heating medium through suitable heat transfer surfaces. It has been found that the heat transfer distance from the surface to the center of solids. particles of fluidizable size is sufficiently small and the heat transer and distribution rate from the heat transfer surface into a. fluidized mass of-solids sufliciently highto permit a satisfactory'heat supply, in general, at temperature differentials between heating medium and fluidized solids mass of between about 75 and-300 F.,- though higher temperature-differentials may be used. The exact temperature differential depends chiefly on the relative size and location of'the heat transfer surface, the heat capacity of the heating medium and the insulation of the equipment.

The heat transfer surfaces are: preferably imbedded in the fluidized solids bed in the-form of conventional heating coils, vertical or horizontal banks of heating tubes, heatingvessels, and'the like. However, the fluidized solids mass may also bemai'ntained within heat'transfer surfaces of suitable cross-section surrounded by the fluid heating medium; Suitable heating media for temperatures'within the approximate range of 7001300F. include refractory oils, such as cracked gas oils and Dowtherm; inorganic'salt mixtures, such as a mixture of sodium nitrate, sodium nitrite and potassiumfnitrate; *molten metals such as lead; mercury-vapors; combustion gases, or the like.

For higher temperatures it is preferred to conduct a delayed combustion within the heat transfer surfaces in such a'manner that heat generation and the temperature" of the'heat transfer surfaces are substantially uniform over the entire extent of the heat transfer surfaces. This may be readily accomplished'for exampl'e,'by a proper control of the flow velocitiesor a suitable distribution of the combustion fuel'and/or the combustion air over the length of the heating tubes. When using highly heat resistant'alloyed steel surfaces, such as nickel chromium'steel surfaces, temperatures as high as 1500 F. and up to about 2000 F. may be attained in this manner. The heat capacity of this type of heating medium may be considerably enhanced by using powdered solid fuel or suspending finely divided inert solids in the combustion gases, the suspended solids serving as heat accumulators.

The heat supply through suitable heat transfer surfaces in accordancewith the present invention eliminates contamination of the volatile conversion products with heating gas, avoids losses Having set forth the general nature and objects, the invention will be best understood from the more detailed description hereinafter, in which reference will be made to the accompanying drawing, wherein Figure 1 is a semi-diagrammatic illustration of a system suitable for carrying out a modification of the present invention wherein heat is supplied to a fluidized solids bed through heat transfer surfaces embedded therein;

Figure 2 is a'similar illustration of the same principal of heat supply specifically adapted to carry out more than one heat treatment at different temperatures; and

Figure 3 illustrates a modification of the invention involving heat supply through heat transfer surfaces containing the fluidized solids mass, the heating medium surrounding the heat transfer surfaces.

Referring now -in detail to- Figure 1,] the numeral Hl'd'esignates a vertical, substantially cylindrical treating vessel designed for fluid solids operation. The cylindrical main section of vessel It is separated'from a conical-bottom section l2 by a perforated distribution plate or grid M. A bank of horizontal heating tubes 1! is arranged across the cylindrical portion ofvessel l0. Tube bank 20 extends preferably from a lower portion beyond the-middle portion of the cylindrical section of vessel 20.

In operation, finely divided solids'havingxa particle size between about 10 and 400 mesh, preferably between 50 and 200 mesh, are supplied to vessel l0 through line I by' any suitable means known per so such as an 'aera'ted'standpipe, a pressurized feed hopper, a mechanical conveyor, etc. (not shown). The solids may be materials carrying volatile substances such as hydrated clay, saturated adsorbents such as charcoal, silica gel, etc., carbonizable materials, or other solids from which volatile products are. to be driven off at high temperatures, or solids which are to be subjected to a uni-form reaction temperature, such as catalysts for. various gas phase reactions, particularly the reformation of hydrocarbons such as methane with steam to form mixtures of CO' and H2 suitable for thehyclrocarbon synthesis, etc.

A suitable, preferably preheated gas, is introduced through line 3 into the conicalbottom section; l2 and enters vessel It) through grid at a superficial velocity of about 0.3-5 ft./sec., preferably 0.5-1.5 ft./sec. adapted to-convert the solids mass invessel [0 into a dense turbulent fluidized solids bed having a well definedupper level L10. While any gas which does not detrimentally affect the desired treatment may be used it is preferred to employ a-gas which will assist in the desired treatment, for instance, by reducing the partial pressure of products to be volatilized. The quantities of gas required for this purpose may vary in general between about 10 to 5,000 cu. ft. per cu. ft. of treating space per minute. The lower value is used where aeration alone is desired, intermediate values where only reduction of partial pressure is desired and the higher values when reaction of the gas with solids takes place.

The heating of the fluidized'solidsbed is effected by tubes 20 arranged in vessel [0 in such a manner as to establish optimum heat transfer to the solids bed. Any type of conventional heat transfer medium which is suitable for the desired temperature range may be used within tubes 20. The heat transfer fluid is preferably admitted through a manifold 22 and passed through tubes 20 in parallel in order to maintain a uniform heat supply to the different portions of the solids bed. The used heating fluid is discharged through manifold 24. Due to the constant agitation and uniform mixing in the fluidized solids bed which resembles a boiling liquid, excellent heat transfer is established within vessel Ill. The heat transfer requirements are reduced considerably by the motion of the solids particles, as compared to the heating of relatively static deaerated powdered masses. Overheating is avoided by the high turbulence of the solids around the tubes. In this manner, the solids bed may be maintained at any desired treating temperature commensurate with the heat resistance of available tube materials.

Vaporous products and fiuidizing gas containing entrained solids fines are withdrawn overhead from level L and passed through a gassolids separation system which may comprise an internal cyclone separator 26 and/or an external electrical precipitator 28, from which separated solids may be returned to vessel I 0 through lines 21 and 29, respectively. Product vapors and overhead gas, substantially free of solids, are either recovered through line 383 or wholly or in part returned through line 32 to line 3 for fluidization and/or further conversion purposes. Separators 26 and/or 28 may also be located downstream of suitable cooling means to avoid equipment failures resulting from excessive temperatures.

Solid products are withdrawn downwardly from the fluidized bed through a suitable downfiow discharge means 35 which is preferably a conventional standpipe aerated through taps 31 in a manner known per se. Other discharge means such as star or screw conveyors, etc. may be employed if desired.

When the system illustrated in Figure 1 is used sel It) contains a finely divided reformer catalyst such as nickel oxide with promotors as magnesia, alumina, etc. of fiuidizable particle size and a mixture of steam and natural gas is introduced through line 3. Tubes are maintained at a temperature of about 1550-1700 F. to establish a suitable reforming temperature of about 1500 F. in the fluidized bed of vessel Ill. The most suitable heating medium for this application of the invention is a burning combustion mixture of fuel and air, preferably carrying suspended finely divided solids to improve the heat transfer coeificient inside tubes 20. These solids may be separated from the flue gas leaving tubes 20 and resuspended in fresh combustion mixture, if desired.

Referring now to Figure 2, I have illustrated therein an embodiment of the invention adapted to carry out 2 heat treatments at dilferent temperatures such as the preheating and carbonization or the two-stage gasification of carbonaceous solids. The latter type of treatment will be used hereinafter to explain the operation of the systern by way of example although other treatments may be carried out in an analogous manner.

The system of Figure 2 essentially comprises a low temperature vessel 23!] and. a high temperature vessel 220 which are provided with vertical heating tube banks 210 and 230, respectively. The shape and general design of vessels 2% and 22!] are similar to that of vessel H) of Figure 1.

In operation, the carbonaceous starting material such as finely divided coke or coal having a for the distillation and, more particularly, the

spent oil shale or tar sand, which is kept at the desired carbonization temperature of about 850- 1100 F. with the aid of tubes The carbonizable material is fed. through line I into the hot dry fluidized solids bed at a rate which will prevent substantial caking within vessel l0. This may be accomplished by maintaining not more than about 10-25% by weight of fresh bituminous solids in the solids bed in vessel H). In case the particles tend. to build up in the course of operation, solids may be removed through line ground and returned through line i to vessel Iii,

Any of the above mentioned heating fluids preheated to a temperature about '75-300 F. higher than the desired carbonization temperature may be used in tubes 26. Steam. inert gases or product gas may serve as fluidization gases preferably at a superficial velocity of about 0.5-1.5 ft. per sec. Carbonization pressures may range from atmospheric to 200 lbs. per so. in. depending on desi n and product cons derat ons; Pressures between about 5 and lbs. per sq. in. are preferred.

It will be understood by those skilled in the art that tubes 29 may be arranged vertically rather than horizontally without deviating from the spirit of the present invention.

The system of Figure 1 may also be used for the reformation of methane or the like with steam to produce synthesis gas. In this case, vesparticle size of preferably less than about mesh is supplied through line 2ill to vessel 200 and maintained therein in the form of a dense turbulent bed having an upper level L200, with the aid of a gas such as steam, CO2, etc. required for the desired gasification reaction and supplied from line 203 through grid 205 at a superficial velocity of about 1-6 ft. per second. Bed densities of about 10 to 40 lbs. per cu. ft. are desirable in vessel 206. The gas quantities required for this purpose may amount to about 40 to 100 cu. ft. per lb. of carbon to be gasified.

Heating tubes 2|!) are maintained at a temperature of about lO00-1200 F. with the aid of hot flue gases recycled from the high temperature tubes 23!] through manifold line 208. If desired, the temperature of these flue gases may be increased by the addition of a combustion mixture of air and fuel supplied through line 209. Spent flue gas is withdrawn from tubes 2| 0 through manifold line 2| I.

At the conditions indicated, the carbonaceous feed in vessel 200 is uniformly heated to a temperature of about 850-l100 F. which is below gasification temperature but sufficient for low temperature carbonization in case a carbonizable feed is used.

A relatively dilute suspension (density about 0.5 to 5 lbs/cu. ft.) of finely divided coke in fiuidizing gas and/or product vapors and gases is carried overhead from level L200 through pipe 2l5 into the lower conical section of vessel 22!] to form therein above grid 2l8, as a result of the reduced gas velocity, a dense fluidized solids bed having a level L220 similar to that maintained in vessel 2%. If desired, additional reacting gas may be supplied through line 2 l6.

Heating tubes 236 are maintained at a temperature of about 1700-1900 F. with the aid of a combustion mixture of fuel and air supplied through manifold line 2|9, and burning atan approximately uniform rate throughout the length .of the heating tubes. The tubes are fired in parallel to give multiple points of heat introduction in the heating tubes. Using 10 to 50% excess air the velocity thru the tubes is maintained above 25 ft./-sec., preferably in the range of 40-75 ft./sec., to afiord delayed combustion and uniform temperatures over the tube length. 'In'this manner the carbonaceous solids in vessel 220 are maintained at a gasification temperature of about 16001800 F. and they react with the fiuidizing gas to form product gas containing H2 and/ or CO which is withdrawn overhead through pipe 235, if desired, after the separation of entrained solids (not shown). Ash may be removed through line 231. However, in many cases it maybe desirable to maintain a high ash content of about l550% in vessel 220 in order to utilize the catalytic activity of the ash. In this case, a suitable proportion of the ash such as .5 to 5 times the quantity of coal fed is recycled through line 239 and thus retained in the system. Any 'carbon removed with the ash through line 231 may be burned in the boiler used for steam production.

When the system of Figure 2 is used for the manufacture of city gas from coal the B. t. u. value of the product gas is greatly enriched by -the.carbonization products obtained in vessel 200. The B. t. u. content of the gas may be further enhanced by operating at such pressures, e. g. about 200-300 lbs. per sq. in., as will favor the formation of methane in the water gas generator. If water gas suitable as feed gas for the catalytic synthesis of hydrocarbons is produced, the ratio .1

of HzzCO may be controlled by the cracking or reaction of the volatile carbonization products from vessel 200 with steam and/or CO2 in vessel 220. Due to the passage of the distillation products of the coal from vessel 200 to vessel 220 which is athigher temperature, tars are cracked so that the gases from vessel 220 contain little or no condensible material. In any case the product yield and quality are utterly unaffected by the method of heat generation. It will also be appreciated that this system is particularly well adapted to the preparation of a highly reactive gasification coke by conducting a low temperature carbonization in vessel 200. In this manner, the actual gasification temperatures in vessel .220 may be lowered by about 100-300 F. without depressing the steam conversion to in- .eificiently .low levels.

Heating tubes 2 I 0 and 230 are shown in a vertical position and shaped like hairpins. Though .horizontal tubes may be used, vertical pipes are usually preferred because the height of the fluidized bed is normally considerably greater 'thanits width. The hairpin shape permits heat expansion and contraction without excessive stresses.

It is also noted that in the two vessel system the greater part of the endothermic heat for the decomposition of the CO2 and/ or H2O is provided in the low temperature reactor 200. This may be as much as 60% of the reaction heat; the second reactor 22!! being employed to complete the reaction of the CO2 and/ or the H20 and to adjust the products to the water gas equilibrium at the higher temperatures. As a result, the exit flue gas temperature is lower than if one vessel is used. Also, much of the heating surface may be of alloys containing less expensive nickel and chromium.

Referring now to Figure 3, the system shown therein is adapted to external heating of the fluidized solids in accordance with the present invention and will be described hereinafter using a two-stage carbonization of coal as an example. However, other fluid solids treatments may be conducted therein.

Two vertical treating vessels 300 and 320 similar in shape to vessels 200 and 220 .are provided, preferably in a superimposed position. Finely divided carbonization coal of fluidizable particle size is fed through line 3! to vessel 300 wherein it forms above grid 305 a dense turbulent bed having an upper level Lane. The solids bed in vessel 300 is fluidized and maintained at a pre-' heating or low carbonization temperature of about TOO -900" F. by a hot dilute suspension of coke in fiuidizing gas and carbonization vapors and gases passing upwardly from vessel 32! through pipe 3 I 5 as will appear more clearly hereinafter.

Volatile carbonization products are withdrawn overhead from level L300, freed of entrained solids in separator 301 and passed through line 309 to a conventional recovery system (not shown). A portion of the gaseous products may be recycled through line 310 to gas feed line 32! of vessel 320.

Preheated or precarbonized fluidized coal is withdrawn downwardly from vessel 300 through a standpipe 3|! aerated with steam, product gas or the like, through taps M8, and introduced into carbonization vessel 320 to form therein a dense turbulent mass of coal and coke fluidized by an inert fiuidizing gas such as steam, CO2, etc., introduced through line 32I and 323, to form an upper level 1020. Gas velocities of about 0.5 to 2.0 ft./sec. are suitable properly to fluidize the solids mass in vessel 320 and to carry volatile and solid carbonization products overhead through pipe 3| 5 at the speed and temperature required for the desired treatment in vessel 300.

In accordance with the invention, the temperature in vessel 320 is maintained at the desired level of, say, about 1l00-1300 F. by means of an external heat supply in heater-furnace 330 which may be operated as follows. Product coke is withdrawn downwardly from vessel 320 through a discharge well 324 to be recovered through branch pipe 325. A portion of the product coke amounting to about 3 to 10 lbs. per 1b. of coal to be carbonized is passed into line.32'l where it is picked up by a carrier gas such as steam, nitrogen or recycle gases supplied through line 329 to form a elatively dilute suspension which flows upwardly through tubes 335 of heater-furnace 330. A combustion mixture of fuel and air is fed to heater 330 through line 331 and flue gases are withdrawn through line 339. The superficial velocity of the suspension in tubes 335 and the rate of combustion in heater-furnace 330 may be readily so controlled that the suspension leaves tubes 335 at any desired temperature which, for the purposes of the present example, lies between about 1300 and about 1500 F. Flow velocities of about 10 to 25 ft. per sec. and furnace temperatures of about 1600 F. are suitable for this purpose in commercial operation. The highly heated coke suspension is returned to vessel 320 through line 340 and transfers its heat to the fluidized bed undergoing carbonization.

It will be understood that instead of passing the suspension through tubes 335 it may flow around tubes 335 which, in this case, may be supplied with the combustion mixture.

The system of Figure 3 may, of course, be used for the manufacture of producer, water or syn- 9, thesis gas by selecting suitable gases supplied through line 323, suitable carbonaceous charge and suitable treating temperatures as will be understood by those skilled in the art.

I have shown two-vessel systems in Figure 2 and Figure 3 and this arrangement has the distinct advantage that more completely treated or reacted solids such as relatively pure ash or dry coke rather than solids of an average degree of treatment may be withdrawn from the system. It will be understood, however, that for many treatments one of the vessels may be omitted or more than two vessels may be used without deviating from the spirit of the invention.

If desired, vertical or horizontal baiiles may be arranged within the treating vessels in order to prevent excessive back-mixing in a vertical direction. Where coal or any other highly coking material is used for gasification or carbonization, it is important that the time of contact of a particle within the first treating vessel averages at least one minute, that is, less than 60 lbs. and preferably about 20-40 lbs. of fresh coal per lb. of material in the vessel should be fed per hour in order to maintain a large quantity of dry material in the vessel and thus to avoid caking and agglomeration of particles. In addition, the dry material will continuously scour the heat transfer surfaces, preventing tar deposits which may interfere with a proper heat transfer.

When carbonaceous materials such as oils, pitches, or asphalts are used as feed materials they may be deposited and treated on fluidized solids such as coke, sand, or the like maintained in the treating vessels.

Other modifications within the scope of my invention will occur to those skilled in the art.

The invention will be further illustrated by the following specific example.

Example In the gasification of a typical gasification coal in a system of the type illustrated by Fig. 2 good results are obtained at the conditions specified below.

Temperature of tubes 210 1400 F. Material of tubes 210 KA S-steel Temperature of vessel 200 1000 If. Pressure in vessel 200 p. s. 1 g Temperature of tubes 230 2000 F Material of tubes 230 NCT steel Temperature of vessel 220 1500" F Pressure in vessel 220 30 p. s 1 g Pressure inside tubes 210 and 23 Coal feed rate to vessel 200 Solids circulation between vessels 200 and 220 Steam rates To vessel 200 150 lbs/sq. ft./hr. To vessel 220 20 p. s. i. g.

100 lbs/sq. ft./hr.

1200 lbs/sq. ft. of vessel 200/hr.

other modifications obvious to those skilled in the;

art are within the scope of my invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

I claim:

1. The method of converting carbonaceous materials into volatile fuels at elevated temperatures within the range of about 700-2000 F. in two essentially endothermic conversion stages carried out in two dense turbulent beds of subdivided solids fluidized by an upwardly flowing gas to resemble a boiling liquid having a well defined upper level, which comprises maintaining one of said beds at a relatively low conversion temperature and the other bed at a relatively high con- Car version temperature, within said range, passing said fiuidizing gas in series first through said bed of low temperature and then through said bed of high temperature, said fiuidizing gas containing constituents reacting endothermically with carbon at said high temperature to produce a fuel gas containing carbon monoxide, feeding fresh carbonaceous materials to said low temperature bed, passing solids from said low temperature bed substantially at said low temperature to said high temperature bed, maintaining said high temperature in said high temperature bedpby contacting the latter with a tubular heating surface heated to a temperature above said high temperature by a fluid combustion mixture burning in contact with said surface separating said bed from said mixture, passing solids from said high temperature bed substantially at said high temperature to said low temperature bed, withdrawing volatile fuels upwardly from the bed last passed through by said fluidizing gas, and withdrawing a discard stream of relatively spent solids from said high temperature bed.

2. The method of claim 1 wherein said combustlon mixture fiows through said tubular surface and the flow velocity of said fiuid combustion mixture is maintained at about 40-75 ft. per second, said combustion mixture containing about 10-50% excess air so as to burn said mixture at a substantially constant rate along said surface and to maintain said surface at a substantially uniform temperature of about 1700-1900 F.

3. The process of claim 1 in which said carbonaceous materials are solid and said high temperature conversion stage comprises the conversion of carbonaceous solids into a fuel gas rich in CO.

4. The method of claim 1 in which said surface consists essentially of a highly heat-resistant alloyed-steel.

5. The method of claim 1 wherein said combustion mixture is a suspension of solids in gases.

6. The method of claim 1 wherein at least two of said beds are maintained in series at different temperatures, heating mixture from said bed of relatively high temperature is passed to a heating surface contacting said bed of relatively low temperature and the carbonaceous feed material is passed countercurrently to said heating mixture through said beds.

7. The method of claim 1 wherein a coking carbonaceous material is used as starting material and the rate of fresh feed of carbonaceous material is so controlled that less than 60 lbs. of fresh material per lb. of solids in said low temperature bed is supplied to said low temperature bed per hour.

8. The method of converting carbonaceous materials into volatile fuels at elevated temperatures of about 700-2000 F. in two essentially endothermic conversion stages carried out in two dense turbulent beds of subdivided solids fluidized by an upwardly flowing gas to resemble a boiling liquid having a well defined upper level, which comprises maintaining one of said beds at a relatively high temperature and the other bed at a relatively low temperature within said range, passing said fiuidizing gas in series first through said bed of low temperature and then through said bed of high temperature, said fiuidizing gas containing constituents reacting endothermically with carbon at said high temperature to produce a fuel gas containing carbon monoxide, feeding fresh carbonaceous solids to said low temperature bed, passing carbonaceous material from said low temperature bed to said high temperature bed in series, maintaining said high temperature in said high temperature bed by contacting the latter with a tubular heating surface heated to a temperature above said high temperature by a fluid heating medium, said surface separating said high temperature bed from said medium, supplying heat to said low temperature bed through a tubular heating surface embedded in said low temperature bed and passing heating medium from said first named surface through said second named surface.

CHARLES E. HEMMINGER.

REFERENCES CITED The following references are of record in the file of this patent:

Number,

Number 12 UNiTED STATES PATENTS Name Date Kerr Feb. 18, 1930 Sabel et a1 Apr. 17; 1934 Odell Dec. 11, 1934 Abrams et a1 Jan. 21, 1947 Fulton Apr. 8, 1947 Watson Mar. 23, 1948 G'ohr' May 24, 1949 FOREIGN PATENTS Country- Date Great Britain May 2, 1929 Great Britain Dec. 31, 1931. 

1. THE METHOD OF CONVERTING CARBONACEOUS MATERIALS INTO VOLATILE FUELS AT ELEVATED TEMPERATURES WITHIN THE RANGE OF ABOUT 700*-2000* F. IN TWO ESSENTIALLY ENDOTHERMIC CONVERSION STAGES CARRIED OUT IN TWO DENSE TURBULENT BEDS OF SUBDIVIDED SOLIDS FLUIDIZED BY AN UPWARDLY FLOWING GAS TO RESEMBLE A BOILING LIQUID HAVING A WELL DEFINED UPPER LEVEL, WHICH COMPRISES MAINTAINING ONE OF SAID BEDS AT A RELATIVELY LOW CONVERSION TEMPERATURE AND THE OTHER BED AT A RELATIVELY HIGH CONVERSION TEMPERATURE, WITHIN SAID RANGE, PASSING SAID FLUIDIZING GAS IN SERIES FIRST THROUGH SAID BED OF LOW TEMPERATURE AND THEN THROUGH SAID BED OF HIGH TEMPERATURE, SAID FLUIDIZING GAS CONTAINING CONSTITUENTS REACTING ENDOTHERMICALLY WITH CARBON AT SAID HIGH TEMPERATURE TO PRODUCE A FUEL GAS CONTAINING CARBON MONOXIDE, FEEDING FRESH CARBONACEOUS MATERIALS TO SAID LOW TEMPERATURE BED, PASSING SOLIDS FROM SAID LOW TEMPERATURE BED SUBSTANTIALLY AT SAID LOW TEMPERATURE TO SAID HIGH TEMPERATURE BED, MAINTAINING SAID HIGH TEMPERATURE IN SAID HIGH TEMPERATURE BED BY CONTACTING THE LATTER WITH A TUBULAR HEATING SUR- 